Lots of anniversaries lately. While it’s still technically summer, let’s contemplate Antarctica. Yet, school has started, so let’s learn of… the entire Solar System. That’s right, if you want to know more about space, go to Antarctica. There are multiple reasons, but meteorites are #1.
Antarctica, as modern Solar System science has taught us, is not merely the top source of meteorites. It doesn’t just outnumber all other sources combined. The fruitful regions of Antarctica have yielded more than twice as many meteorites as the entire rest of the world, combined. We just learned of this in the 1969-1970 field season, when by pure luck a Japanese research expedition brought in the first bounty of space samples.
Before the JARE team (Japanese Antarctic Research Expedition) left, senior scientist Masao Gorai stated that Antarctica’s rocks were now boring, and that he would like a meteorite. (He later claimed he wasn’t being completely serious.) The team, in the course of other fieldwork, happened upon three unusual rocks in one day. Suspecting some might turn out to be meteorites, they took notes and carefully stored them. By the end of the field campaign in a few weeks, they had nine suspected meteorites. Much to Gorai’s surprise, every one of the nine was extraterrestrial, and not fragments of one object, either.
Antarctic specimens now dominate the meteorite collections of multiple countries. This “treasure trove” has given us lunar and martian rocks, and rare ones that get degraded or destroyed in other areas of the Earth. No exaggeration: Antarctica upended planetary science.
The 1969-70 field team arrived at the Antarctic shore- Japan’s Syowa base- in late October. After mustering all their gear and supplies, they departed in November, via tracked snow vehicles, for inland ice fields. Reaching their planned work area near the Yamato mountain range, they began traverses, taking logs and stopping for site measurements. On Dec. 21, three separate stones were found, and collected as potential meteorites; it was already palpable that dark rocks in the middle of an ice field were unusual somehow. Six more rocks followed.
By the summer of 1970, the nine had gotten to Masao Gorai. After some prodding, he finally examined them, and wrote back to the expedition crew: “All were found to be meteorites! …This is indeed a natural “Meteorite Museum” that made me extremely amazed and shocked.”
It had been suspected that meteorites, falling on permanently-frozen terrain, would be preserved and accumulated, awaiting discovery. By the end of the expedition, the field scientists proposed a second reason for the abundance. Many ice fields creep slowly. When a mass of ice meets an obstacle like a mountain, it ramps up. The protruding ice is vulnerable to loss via sunlight, wind scouring, etc. The ice field is then a natural conveyor belt. Meteorites slowly gather on and in the ice, and are taken to the uphill slope. As the ice erodes, its rocks are not melted but released. These areas before ice obstacles are now called “stranding zones” or “stranding surfaces,” and have orders of magnitudes more meteorites than an equal area anywhere else. Meteorite hunters simply walk (/snowmobile) the ice and pick them up.
Gorai published his results in a Japanese geology journal, MAGMA, that August. However, attention did not arrive from outside Japan, until 1973’s meeting of the Meteoritical Society, in Davos, Switzerland. Delivering their results before the audience, and not in Japanese, the revolution really began. (An English-language journal, Earth and Planetary Science Letters, also put forth a research paper on it.) Geologist William Cassidy, from Case Western Reserve University, realized like Gorai that a rich bounty of samples lie in wait. He immediately drafted a grant proposal for a US expedition to get meteorites… and was turned down.
Japanese researchers were more fortunate. By then, the Antarctic concentration mechanism had drawn the attention of staff at NIPR (National Insitute of Polar Research). An expedition for the 1973-74 season was approved, for the explicit purpose of meteorite collection. They retrieved six hundred thirty three. It would not be until 1976-77 that Cassidy would receive funds for a US equivalent, and even that would be a joint US-Japan project.
US expeditions were managed by Cassidy’s Case Western Reserve University, but their samples would be received and curated by two meteorite-leading institutions. Both the Smithsonian Institute, and NASA’s Johnson Space Center, already had handling facilities and expert staff. In addition, Cassidy specified that further meteorite studies could be performed by qualified applicants from any institution- that is, US-recovered samples would not be proprietary to NASA or the Smithsonian, let alone his own CWRU. This allowed top researchers- from anywhere they might affiliate- to do top work. Cassidy realized this would reap the best science from the best-preserved samples. There would be no stampede in Antactica, due to hoarding at home. Conspiracy theorists take note: you’re not being kept out of the loop. More likely, you’re not qualified to be awarded a space sample (versus experienced meteoriticists), or (more mundanely) you don’t even know where to begin the application process.
Either way, the torrent of stones had begun. By the 2000-01 season, Antarctic finds numbered ~3500; by 2009, it was ~45,000. While the Japanese tended to visit the coastal mountains near the Japanese base, other countries opened up exploration of the Transantarctic mountains. This vast mountain range was mostly less accessible, but contained numerous individual stranding areas to search. Later years delivered the first lunar meteorite ever found (ALH 81005), then the first Martian meteorite to be identified as such (EET 79001).
(This explains why lunar meteorites had not been found earlier, despite the fact that lunar material should be able to make the trip more easily than, e. g., Martian rock. Lunar rock, being both differentiated magma, and formed when a giant impact struck the Earth, is essentially Earth rock, secondhand. A moon rock is so Earthlike and boring, lunar meteorites actually were being “found,” but not recognized as being meteorites at all and dismissed. It is only on an ice field that a rock- Earth petrologies or not- is worthy of note, and given a closer look.)
In the intervening years, we have not only found rare CI meteorites in Antarctica, but as many CIs as the rest of the world, combined. That’s not hard to do, as ‘rest of world combined’ was only five meteorites. We even suspect that the Antarctic CIs may be a separate but related meteorite group. Since CIs are vulnerable to water and weather on Earth, all of those five were found soon after they were witnessed as meteor entries. Antarctic CIs, on the other hand, are quickly frozen, and stabilized against crumbling or washing away. It is thus likely and probable that Antarctic CIs are tens of thousands of years old, and from a different parent body in space than the non-Antarctic, modern CIs.
There’s more, in number if not in grams. Micrometeorites are falling constantly, without being noticed. They are small enough that the meteor streak associated with their high-speed flight through the air is dim, or even nonexistent. Yet micrometeorites are everywhere- one meteoriticist estimates that they fall at a spacing of roughly one per square meter, given a reasonable collection time for that square meter. We don’t notice because “MMs” are a few microns to one millimeter across, and to you and me just look like dust. The real issue is separating extraterrestrial samples from everyday contaminants.
Antarctica isn’t everyday, by any way. Micrometeorites have been collected from ice lakes, deliberately-melted ice masses, and even the melting well one base needs for its drinking and washing water. Since there are far fewer industries, and close to zero soil patches, the micrometeorites can be spotted by eye (well, after a microscope or strong eye loupe). There isn’t the ridiculous burden of sifting through ordinary dust like there is in the rest of the world.
Don’t dismiss micrometeorites because ‘it’s just dust.’ It is because they are small that they survive passage through the atmosphere, and impact with the surface. MMs may contain comet samples, too fragile to survive and be recovered in the form of macroscopic meteorites.
If you want to study the Solar System, there’s no way around (or over) it: you have to get hold of some Antarctic material at some point. It is not out of place at all to say, as one of the original Japanese field scientists did, that “For planetary science… as important as the first human landing on the moon”. [Yoshida, M. 2010 Polar Science 3, p. 272-84]
Stone Sweet Stone 